This invention relates to a center posts for tire curing presses and more particularly, to an extendable center post for a tire curing press.
It is well-known in the art to shape and cure tire carcasses in a mold using a bladder that contains the internal curing heat medium and pressure within the carcass to hold the exterior of the latter in contact with a tire mold during the curing process. Conventional standing post tire curing presses utilizing bladders typically comprise a bladder assembly and a tire mold assembly. FIGS. 1 and 2 depict such a tire curing press. The bladder assembly typically includes a fixed center post and a bladder clamped between upper and lower clamp ring assemblies that are opposite each other along the center post. The upper clamp ring assembly often includes an upper mold ring and an upper clamp ring. The lower clamp ring assembly generally includes a lower bead ring and a lower clamp ring.
While such systems are generally effective, most suffer from excessive production of defective product due to damage to the bladders. The damage occurs largely due to the fact that most fixed center posts are fixed at the height of the final cured product. However, most green tire assemblies are wider axially bead-to-bead than the final cured product. As such, when the green tire assembly is loaded over the center post, there is a distinct gap between the upper bead of the tire assembly and the upper clamp ring for the bladder. Thus, when the bladder is initially inflated prior to closure of the mold, the section of the bladder from the green tire assembly upper bead and the upper clamp ring remains exposed. FIG. 1 shows this situation wherein the tire press using a fixed height center post is in a position to receive the green tire carcass. As can be seen, the bladder balloons upward from the upper clamp ring.
The upper part (cavity) of the mold is then lowered over the green tire assembly until the mold contacts the upper mold ring on the center post. However, during the lowering of the mold, the green tire assembly is pressed down and often the exposed section of bladder may fold over and get pinched between the mold and the upper mold ring, as shown in FIG. 2. Over time, the bladder tends to be cut after repeated pinching causing the bladder to leak, and not to hold sufficient pressure during the tire curing process. When the bladder leaks, tires tend to be produced which have poor inside finish, poor bead formation or other defects that tend to reduce manufacturing yields and increase the number of defective tires produced. Additionally, damaged bladders ultimately result in higher maintenance and replacement costs associated with such tire presses.
What is desired, therefore, is a center post assembly for a tire curing press that substantially eliminates pinching of the bladder prior to closing of the tire mold.
What is desired, therefore, also is a tire curing press incorporating a center post assembly that substantially eliminates pinching of the bladder prior to closing of the tire mold.
What is desired, therefore, also is a method of manufacture of a tire using a tire curing press incorporating a center post assembly that substantially eliminates pinching of the bladder prior to closing of the tire mold.
Accordingly, it is an object of the invention to provide a center post assembly that reduces pinching of the bladder between the mold and center post during mold closure.
Another object of the invention is to provide a center post of the above character that reduces the possibility of pinching of the bladder related to action of the center post.
A further object of the invention is to provide a center post of the above character having reduced pneumatic and hydraulic parts.
A still further object of the invention is to provide a center post assembly of the above character of simplified construction to facilitate maintenance and replacement.
A still further object of the invention is to provide a tire curing press incorporating a center post assembly that substantially eliminates pinching of the bladder prior to closing of the tire mold.
A still further object of the invention is to provide a method of manufacture of a tire using a tire curing press incorporating a center post assembly that substantially eliminates pinching of the bladder prior to closing of the tire mold.
These and other objects of the invention are achieved by provision of a center post assembly for a tire curing press comprising a center post having a upper component disposed above a lower component. The upper component is movable between a first position wherein the upper component is adjacent to the lower component and a second position wherein the upper component is axially displaced away from the lower component and substantially adjacent to an upper bead of a green tire assembly. The center post assembly further includes a bladder sealingly clamped to the upper and lower components. The bladder is in fluid communication with a fluid supply. The upper component moves between said first and second positions due to expansion of the bladder caused by introduction of fluid into the bladder from the fluid supply allowing the bladder to evenly disperse on the inner surface of the green tire assembly substantially reducing the risk of the bladder being damaged by the mold as it closes.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.